WASHINGTON » So-called lone-wolf terrorists can kill a lot of people at one time, and stopping them presents a nightmare for counterterrorism authorities.

The Obama administration has emphasized battling Islamic State terrorists in their stronghold in Iraq and Syria. But some recent attackers, perhaps including the one in France Thursday night, have had minimal or no contact with the terror group’s hierarchy. They can be driven by factors other than ideology, including suicidal tendencies and deep alienation, experts said.

That means destruction of the Islamic State won’t necessarily diminish the occurrence of attacks, experts said. Some lone-wolf terrorists are motivated by other factors, including social alienation and mental instability.

“I do think we shouldn’t second guess the value of degrading the Islamic State in its stronghold,” said Max Abrahms, a political scientist and terrorism expert at Northeastern University in Boston. “The brand will suffer. They will have a more difficult time attracting recruits.”

At the same, he said, “Its capability goes down but its motivation for attack goes up.”

The attack along the French seaside promenade in Nice Thursday night apparently was carried out by a lone Frenchman of Tunisian descent who used a truck as his main weapon.

“Lone wolf attackers can indeed be very bloody even in countries where access to guns is restricted, like in France,” said Abrahms, who described the Bastille Day massacre in Nice as “arguably the most lethal lone-wolf attack ever.”

In addition to killing 84 people, the 31-year-old truck driver, identified by French officials as Mohamed Lahouaiej Bouhlel, injured 200 other people, 54 of them critically.

The perpetrator had a background of petty crimes, and is not known to have had accomplices. Authorities pored over his background Friday in a search for terrorist ties and acknowledged he was on no terror watch lists.

“French investigators are still looking very closely at what sort of connections this individual may have to extremist organizations,” White House spokesman Josh Earnest said. “There have been no claims of responsibility that we have seen thus far, but we’ll obviously look to that as a potential clue about what may have contributed to this particular terrorist attack.”

The French attack came a little more than a month after another lone wolf, American-born Omar Mateen, who was possibly inspired by Islamic State extremism, killed 49 people at a gay nightclub in Orlando, Fla., in the deadliest terror attack on U.S. soil since the Sept. 11 terror attacks in 2001. Mateen used a semi-automatic rifle and a pistol.

Lone-wolf killers often have criminal histories and suicidal tendencies, experts said.

“I’ve coined the term the ‘loon wolf’ rather than the lone wolf to denote the fact that many of these attackers suffer from mental instability,” Abrahms said.

The Islamic State, known as ISIS, did not immediately claim responsibility for the Nice attack, although its spokesmen have long urged sympathizers to mow infidels down with vehicles or kill them with brute force.

An ISIS spokesman, Abu Mohammed al-Adnani, urged followers in 2014 to take action against any enemy: “Smash his head with a rock, or slaughter him with a knife, or run him over with your car, or throw him down from a high place, or choke him, or poison him.”

“In some cases, the organization doesn’t even know who the person is until after the attack,” Abrahms said. “The Islamic State is happy to claim attacks by people who really may be suffering from mental illness and are not necessarily religious in accordance with Islam.”

Lone-wolf attacks are not just the province of Muslim radicals.

Five years ago, a Norwegian right-wing extremist went on a rampage in the capital of Oslo and at a summer camp on a nearby island, claiming a total of 77 lives in the deadliest attack in Norway since World War II. The extremist, Anders Behring Breivik, used a car bomb and a semi-automatic weapon.

“There are multiple motivations at play when people perpetrate these kinds of actions,” said Eric Cleven, an expert on transnational terrorism at Saint Anselm College in New Hampshire. One of the factors is social alienation.

“If we have friends and loved ones and family, we don’t sit and think about how we can kill 150 people,” Cleven said.

While not strictly lone wolves, a husband and wife couple perpetrated a terrorist attack in San Bernardino, Calif., on Dec. 2, 2015, shooting and killing 14 people and wounding 22 others. To date no evidence has surfaced that they had contact with the Islamic State.

In some cases, perpetrators have no direct contact with terror groups, but grow more radical by watching videos or reading radical tracts on the internet.

“It allows an individual anywhere to come across terrorist group web pages and enter chat rooms,” said Jeffrey D. Simon, a visiting lecturer at the University of California, Los Angeles and author of “Lone Wolf Terrorism: Understanding the Growing Threat.”

Many lone terrorists are loners — but not in the virtual world.

“They still have the tendency to want to talk. They may not talk to other individuals, but they’ll post in internet chat rooms,” Simon said. “In the Orlando shooting, the shooter there was looking on Facebook during the attack to see how this was playing out.”

The lone-wolf phenomenon presents a huge challenge to law enforcement and counterterrorism officials, experts said. Monitoring their communications may not turn up direct contact with terror higher-ups — those links don’t exist — and surveillance may not offer many other clues to their plans.

“We can’t just create a Fortress America and a 24/7 surveillance system,” Simon said.

Moreover, soft targets of crowds are common in Western countries.

“He just needed to have a truck,” Simon said of the French attacker.

Simon said the lone-wolf phenomenon will not go away soon.

“I see it lasting, not even for years, I see it for decades,” he said.

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(Lesley Clark contributed to this report.)

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©2016 McClatchy Washington Bureau